Last week I bought a used 2011 iSonic. I checked the board for damages and wether it has got soft or not. All looked ok, but then 2 days later I noticed a crack! I feel really stupid now, because it is quite obvious:

www.chumba.ch/images/crack.jpg

I stood on the left and right side of the crack and it seems to me, that it is just the top layer of the sandwich, which got apart. The weight with footstraps is around 6.6-6.7kg, so I assume there is no water inside.

I read that the 2011 models use UD Carbon 80 and 60g glass. How would you fix that? Do I have to take off/grind off about 5 cm on each side of the crack and then laminate 1 or 2 layers of 60g glass fiber (10cm wide) on top of it? I read that it should not be stronger after the fix to avoid hard spots.

sand it down, and repair the sandwich with PU-glue, if the bottom laminate is broken, it will be more work!
I would use a 6cm wide carbon strip and a10cm wide glass strip put the glas on top of the carbon, so its easier to sand out smooth,
The rail looks ok, since most of the strength is there.
If the guy who sold it to you knew about the damage and said nothing, i would demand a refund or compensation!
Check the bottom, rocker( with a long straight ruler) and check for water!

I would use 200g/mē carbon and 100 or 160g/mē twill glass, because that is what i have in the garage. It dosent matter, as long as you sand properly, so the new laminate has good contact with the old laminate. Use strong tape and perhaps peel-ply to create pressure. best would be with vaccum pump , but not necessary for such a small damage.

Beware of epoxy! use double latex gloves when you use it, never breathe the sanding dust.